There's currently 2 characters you can recruit, but they stated that they'll add more in the future. They have set personalities and you can improve your rapport with them by doing stuff they like while questing with them. For example, one of them hates goblins, so she will appreciate you more if you kill goblins. You can improve their combat abilities just by adventuring with them, and you can assign them to be a healer, a tank or a damage dealer. They can't exactly replace a good player, but they still make stuff like solo'ing group dungeons easier.
Their personalities/looks are set, but you can still craft them a custom outfit or assign them a costume that you own. You can also choose which mount they use.